Numerous clasps are known for bracelets, in particular for wristwatches or for jewellery, which comprise unfolding moveable strands.
In many clasps, called triple clasps, i.e. including two strands hinged to a buckle on which they are folded down, each strand including a pin cooperating in a locking position with one eye of the buckle, the buckle is fitted with two resiliently mounted pushers. Often, pressure on only one of the two pushers can cause the clasp to open, which is unsatisfactory from a safety viewpoint. Likewise, after a first strand has been locked, it is common for the closing of the other strand to have the effect, by separating the pushers, of releasing the strand which was already locked and which was providing provisional security. Certain designers have overcome this latter defect by setting a sequential closing order of the strands, which is inconvenient for the user.
Various clasp devices propose solutions to this problem. Thus CH Patent No. 670 941 in the name of CORNU & CIE SA discloses a clasp with a small number of components, which utilises the elastic deformation of pusher branches in the shape of tuning forks, the ends of which form retaining stops for the strands. EP Patent No. 0 549 846 in the name of GTF SRL discloses a bolt device comprising bolts, having concave paths on which a V-shaped spring abuts, which project outside a case to cooperate with hooks comprised in the strands, and for unlocking, a single pusher pushes ramps comprised in these bolts, against the spring which works by buckling. JP Patent No. 9000320 in the name of CITIZEN discloses a clasp with four bolts each provided with a ramp-shaped cam, arranged in pairs opposite springs and operated against these springs by two pushers each comprising two antagonistic ramps.
CN Patent No. 201278878Y in the name of HUADONG GUAN presents a clasp with two pushers pushed back by a first spring, each carrying two claws pushed outwards by a spring perpendicular to the first spring.
In short, the solutions proposed are often complex or fragile, since they are essentially based on the elasticity of certain components.